Storage medium for data with improved dimensional stability

ABSTRACT

This disclosure relates to a data storage medium, and in particular to a data storage medium comprising at least one high modulus layer used to control the overall degree of flatness in the storage medium.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/683,500,filed Jan. 9, 2002, now U.S. Pat. No. 6,716,505 which is herebyincorporated by reference in its entirety.

This application claims priority to and the benefit of the filing dateof U.S. Provisional application No. 60/316,534, filed Aug. 31, 2001 andentitled STORAGE MEDIUM FOR DATA.

BACKGROUND OF INVENTION

This disclosure relates to a data storage medium, and in particular to adata storage medium comprising at least one high modulus layer used tocontrol the overall degree of flatness in the storage medium.

An increase in data storage density in optical data storage media isdesired to improve data storage technologies, such as, but not limitedto, read-only media, write-once media, rewritable media, digitalversatile media and magneto-optical (MO) media.

As data storage densities are increased in optical data storage media toaccommodate newer technologies, such as, but not limited to, digitalversatile disks (DVD) and higher density data disks for short and longterm data archives such as digital video recorders (DVR), the designrequirements for the transparent component of the optical data storagedevices have become increasingly stringent. Optical disks withprogressively shorter reading and writing wavelengths have been theobject of intense efforts in the field of optical data storage devices.Materials and methods for optimizing physical properties of data storagedevices are constantly being sought. Design requirements for thematerial used in optical data storage media include, but are not limitedto, disk flatness (e.g., tilt), water strain, low birefringence, hightransparency, heat resistance, ductility, high purity, and mediumhomogeneity (e.g., particulate concentration). Currently employedmaterials are found to be lacking in one or more of thesecharacteristics, and new materials are required in order to achievehigher data storage densities in optical data storage media. Diskflatness, also referred to as tilt, is a critical property needed forhigh data storage density applications. Consequently, a long felt yetunsatisfied need exists for data storage media having improveddimensional stability and minimal tilt.

SUMMARY OF INVENTION

In one embodiment, the present disclosure is drawn to an asymmetricoptical storage medium comprising a layer, which improves dimensionalstability in said medium, wherein the asymmetric optical storage mediumcomprises at least one substrate layer, at least one data layer, atleast one high modulus layer, and at least one thin film layer.

In another embodiment, the present application is drawn to a method fordecreasing the tilt of an asymmetric optical storage medium, said methodcomprising an addition step wherein a high modulus layer is added to anoptical storage medium so that the directional stability of said mediumis increased.

BRIEF DESCRIPTION OF DRAWINGS

Various features, aspects, and advantages of the present disclosure willbecome apparent with reference to the following detailed description,appended claims, and accompanying figures.

FIG. 1 is a cross sectional view of one embodiment of the present datastorage medium (10), wherein the medium comprises a substrate layer(20), which is in direct contact with a data layer (30), a data layer(30), which is in direct contact with a high modulus layer (40), and ahigh modulus layer (40), which is in direct contact with a thin filmlayer (50).

FIG. 2 is a cross sectional view of another embodiment of the presentdata storage medium (60), wherein the medium comprises a substrate layer(70), which in direct contact with a data layer (80), a data layer (80),which is in direct contact with a thin film layer (90), and a thin filmlayer (90), which is in direct contact with a high modulus layer (100).

DETAILED DESCRIPTION

The present disclosure describes the use of polymeric material asstorage media for data. In one embodiment of the present disclosure, thestorage medium for data (part 10 in FIG. 1; part 60 in FIG. 2) comprisesa plurality of layers comprising at least one substrate layer, at leastone data layer that is in direct contact with the substrate layer, atleast high modulus layer, and at least one thin film layer. As usedherein, the term “high modulus” refers to a tensile modulus typicallygreater than about 1 Gigapascal (Gpa). The high modulus layereffectively increases the dimensional stability of the data storagemedium by reducing the tilt of the data storage medium. As used herein,the term “tilt” refers to the number of radial degrees by which a datastorage medium bends on a horizontal axis, and is typically measured asthe vertical deviation at the outer radius of the storage medium.Typically, the tilt is half of the average radial deviation (thedeviation of a laser beam) as measured in degrees.

In the context of the present disclosure, a typical data storage mediumis composed of a plurality of polymeric components, which are generallycombined in overlaying horizontal layers of various thicknesses,depending on the specific properties and requirements of the datastorage medium. A major component of a data storage medium is asubstrate layer (part 20 in FIG. 1; part 70 in FIG. 2). The substratelayer is typically made of a polymeric material, which comprises atleast one member selected from the group consisting of a thermoplastic,a thermoset, and any combination thereof. Both addition and condensationpolymers are suitable for the present invention. As used herein the term“thermoplastic polymer”, also referred to in the art as a thermoplasticresin, is defined as a material with a macromolecular structure thatwill repeatedly soften when heated and harden when cooled. Illustrativeclasses of thermoplastic polymers include, but are not limited to,styrene, acrylics, polyethylenes, vinyls, nylons, and fluorocarbons. Asused herein the term “thermoset polymer”, also referred to in the art asa thermoset resin, is defined as a material which solidifies when firstheated under pressure, and which cannot be remelted or remolded withoutdestroying its original characteristics. Illustrative classes ofthermoset polymers included, but are not limited to, epoxides,malamines, phenolics, and ureas.

Illustrative examples of thermoplastic polymers which are suitable forthe substrate layer include, but are not limited to, olefin-derivedpolymers (e.g., polyethylene, polypropylene, and their copolymers),polymethylpentane; diene-derived polymers (e.g., polybutadiene,polyisoprene, and their copolymers), polymers of unsaturated carboxylicacids and their functional derivatives (e.g., acrylic polymers such aspoly(alkyl acrylates), poly(alkyl methacrylates), polyacrylamides,polyacrylonitrile and polyacrylic acid), alkenylaromatic polymers (e.g.,polystyrene, poly-alpha-methylstyrene, polyvinyltoluene, andrubber-modified polystyrenes), polyamides (e.g., nylon-6, nylon-6,6,nylon-1,1, and nylon-1,2), polyesters; polycarbonates; polyestercarbonates; polyethers such as polyarylene ethers, polyethersulfones,polyetherketones, polyetheretherketones, polyetherimides; polyarylenesulfides, polysulfones, polysulfidesulfones; and liquid crystallinepolymers. In one embodiment, the substrate layer comprises athermoplastic polyester. Suitable examples of thermoplastic polyestersinclude, but are not limited to, poly(ethylene terephthalate),poly(1,4-butylene terephthalate), poly(1,3-propylene terephthalate),poly(cyclohexanedimethanol terephthalate), poly(cyclohexanedimethanol-co-ethylene terephthalate), poly(ethylenenaphthalate), poly(butylene naphthalate), and polyarylates.

In another embodiment the substrate layer comprises a thermoplasticelastomeric polyesters (TPE's). As defined herein, a thermoplasticelastomer is a material that can be processed as a thermoplasticmaterial, but which also possesses some of the properties of aconventional thermoset resin. Suitable examples of thermoplasticelastomeric polyesters include, but are not limited to, polyetheresters,poly(alkylene terephthalate), poly[ethylene terephthalate], poly[butylene terephthalate]), polyetheresters containing soft-blocksegments of poly (alkylene oxide) particularly segments of poly(ethyleneoxide) and poly(butylene oxide), polyesteramides such as thosesynthesized by the condensation of an aromatic diisocyanate withdicarboxylic acids, and any polyester with a carboxylic acid terminalgroup.

Optionally, the substrate layer can further comprise at least onedielectric layer, at least one insulating layer, or any combinationsthereof. The dielectric layer(s), which are often employed as heatcontrollers, typically have a thickness between about 200 Å and about1,000 Å. Suitable dielectric layers include, but are not limited to, anitride layer (e.g., silicone nitride, aluminum nitride), an oxide layer(e.g. aluminum oxide), a carbide layer (e.g., silicon carbide), and anycombinations comprising at least one of the foregoing and any compatiblematerial that is not reactive with the surrounding layers.

In the context of the present disclosure, a typical data storage mediumfurther comprises at least one data layer (part 30 in FIG. 1; part 80 inFIG. 2). The data layer, which typically comprises a reflective metallayer, can be made of any material capable of storing retrievable data,such as an optical layer, a magnetic layer, a magneto-optic layer. Thethickness of a typical data layer can be up to about 600 Angstroms (Å).In one embodiment, the thickness of the data layer is up to about 300 Å.The information which is to be stored on the data storage medium can beimprinted directly onto the surface of the data layer, or stored in aphoto-, thermal-, or magnetically-definable medium which has beendeposited onto the surface of the substrate layer. Suitable data storagelayers are typically composed of at least one material selected from thegroup consisting of, but are not limited to, oxides (e.g., siliconeoxide), rare earth element-transition metal alloys, nickel, cobalt,chromium, tantalum, platinum, terbium, gadolinium, iron, boron, organicdyes (e.g., cyanine or phthalocyanine type dyes), inorganic phase changecompounds (e.g., TeSeSn or InAgSb), and any alloys or combinationscomprising at least one of the foregoing.

The reflective metal layer(s) should be of a thickness that issufficient to reflect an amount of energy, which is sufficient to enabledata retrieval. Typically, a reflective layer has a thickness up toabout 700 Å. In one embodiment the thickness of the reflective layer isin between about 300 Å and about 600 Å. Suitable reflective layersinclude, but are not limited to, aluminum, silver, gold, titanium, andalloys and mixtures comprising at least one of the foregoing. Inaddition to the data storage layer(s), dielectric layer(s), protectivelayer(s), and reflective layer(s), other layers can be employed such aslubrication layer(s), adhesive layer(s) and others. Suitable lubricantlayers include, but are not limited to, fluoro compounds such as fluorooils and greases.

In the context of the present disclosure, a typical data storage mediumfurther comprises at least one high modulus layer (part 40 in FIG. 1;part 100 in FIG. 2). In one embodiment of the present disclosure, asuitable high modulus layer typically comprises a thermoset polymer,which can be cured thermally, cured by ultraviolet (UV) radiation, orcured by any method commonly known to those skilled in the art. Inanother embodiment of the present disclosure, the high modulus layercomprises a thermoplastic polymer. In yet another embodiment of thepresent disclosure, the high modulus layer comprises a combination of athermoset polymer and a thermoplastic polymer. Typically, the highmodulus layer is applied to the storage medium via a spin-coatingprocess, however, any method known to those skilled in the art such as,but not limited to, spray deposition, sputtering, and plasma depositioncan be used to deposit a high modulus layer with a thickness in a rangebetween about 0.5 micron and about 30 microns onto the data storagemedium. Illustrative examples of thermoset polymers include, but are notlimited to, polymers derived from silicones, polyphenelene ethers,epoxys, cyanate esters, unsaturated polyesters, multifunctional allylicmaterials, diallylphthalate, acrylics, alkyds, phenol-formaldehyde,novolacs, resoles, bismaleimides, melamine-formaldehyde,urea-formaldehyde, benzocyclobutanes, hydroxymethylfurans, isocyanates,and any combinations thereof. In one embodiment, the thermoset polymerfurther comprises at least one thermoplastic polymer, such as, but notlimited to, polyphenylene ether, polyphenylene sulfide, polysulfone,polyetherimide, or polyester. Typically, the high modulus layer is acopolycarbonate ester. The thermoplastic polymer is typically combinedwith a thermoset monomer mixture before curing of said thermoset. Inaddition the high modulus layer may be added during the laminationprocess of the pressure sensitive adhesive.

Currently, the dimensions of the storage medium are specified by theindustry to enable their use in presently available data storage mediumreading and writing devices. The data storage medium typically has aninner diameter in a range between about 15 mm and about 40 mm and anouter diameter in a range between about 65 mm and about 130 mm, asubstrate thickness in a range between about 0.4 mm and about 2.5 mmwith a thickness up to about 1.2 mm typically preferred. Other diametersand thickness may be employed to obtain a stiffer architecture ifnecessary.

The storage medium described herein can be employed in conventionaloptic, magneto-optic, and magnetic systems, as well as in advancedsystems requiring higher quality storage medium, areal density, or anycombinations thereof. During use, the storage medium is disposed inrelation to a read/write device such that energy (for instance,magnetic, light, electric, or any combination thereof) is in contactwith the data layer, in the form of an energy field incident on the datastorage medium. The energy field contacts the data layer(s) disposed onthe storage medium. The energy field causes a physical or chemicalchange in the storage medium so as to record the incidence of the energyat that point on a data layer. For example, an incident magnetic fieldmight change the orientation of magnetic domains within a data layer oran incident light beam could cause a phase transformation where thelight heats the point of contact on a data layer.

Numerous methods may be employed to produce the storage mediumincluding, but not limited to, injection molding, foaming processes,sputtering, plasma vapor deposition, vacuum deposition,electrodeposition, spin coating, spray coating, meniscus coating, datastamping, embossing, surface polishing, fixturing, laminating, rotarymolding, two shot molding, coinjection, over-molding of film,microcellular molding, and combinations thereof. In one embodiment, thetechnique employed enables in situ production of the substrate havingthe desired features, for example, pits and grooves. One such processcomprises an injection molding-compression technique where a mold isfilled with a molten polymer as defined herein. The mold may contain apreform or insert. The polymer system is cooled and, while still in atleast partially molten state, compressed to imprint the desired surfacefeatures, for example, pits and grooves, arranged in spiral concentricor other orientation, onto the desired portions of the substrate, i.e.,one or both sides in the desired areas. The substrate is then cooled toroom temperature.

The following examples are included to provide additional guidance tothose skilled in the art in practicing the claimed invention. Theexamples provided are merely representative of the present disclosure.Accordingly, the following examples are not intended to limit theinvention, as defined in the appended claims, in any manner.

EXAMPLES

Circular data storage disks were prepared as follows. A substrate layerof 4,4′-isopropylidenediphenol-polycarbonate polymer (BPA-PC) was moldedinto circular disks about 1.1 mm thick, and with an inner radius ofabout 15 mm and an outer radius of about 120 mm. A metallic data layer,of about 500 Angstroms thick, was sputtered to one of the surfaces ofthe BPA-PC substrate disks. Various thicknesses, described in table 1,of an acrylic lacquer layer (Daicure SD-698) were spin coated onto themetallic data layer of the disks, and the lacquer was cured using UVradiation. A co-polycarbonate-ester thin film of about 75 micronthickness, was bonded to the acrylic layer of the disks using a 25micron thickness pressure sensitive adhesive of negligible modulus, toyield circular data storage disks with a layer configuration similar tothat disclosed in FIG. 2. The data storage disks were equilibrated in anenvironment of an humidity of about 50%. The data storage disks werethen transferred from this first environment of an initial humidity ofabout 50%, to a second environment with humidity of about 90%. The tiltof the data storage disks was measured over time at a radius of 55 mmwhile the disk equilibrated in the 90% humidity. The results of themaximum radial tilt measured over the dynamic as the disksre-equilibrated to the 90% humidity environment for the data storagedisks with varying thickness of the spin-coated high modulus layer aredescribed in table 1.

TABLE 1 Maximum High Modulus Radial tilt at Lacquer thickness 55 mm(microns) (degrees) 0 0.316 6.6 0.196 14.6 0.127 27.1 −0.171

As disclosed by the results in table 1, the addition of the high moduluslacquer layer to the data storage disks reduces the radial tilt of thedisks during the dynamic period during which the data storage disks areequilibrating from the first to the second humidity level.

While the invention has been illustrated and described, it is notintended to be limited to the details shown, since various modificationsand substitutions can be made without departing in any way from thespirit of the present disclosure. As such, further modifications andequivalents of the invention herein disclosed can occur to personsskilled in the art using no more than routine experimentation, and allsuch modifications and equivalents are believed to be within the spiritand scope of the disclosure as defined by the following claims.

1. An asymmetric optical storage medium comprising a plurality oflayers, said plurality of layers including a substrate layer, a datalayer, and at least one high modulus layer which improves dimensionalstability in said medium, said high modulus layer comprising a curedhigh modulus organic polymer having a tensile modulus of at least 1gigapascal.
 2. The optical storage medium of claim 1, wherein said highmodulus layer comprises a material cured using ultra-violet light. 3.The optical storage medium of claim 2, wherein said material comprisesat least one member selected from the group consisting of an acrylate,an epoxy, a silicone-acrylate, a urethane, and any combination thereof.4. The optical storage medium of claim 1, wherein said high moduluslayer comprises a thermally cured material.
 5. The optical storagemedium of claim 4, wherein said material comprises at least one memberselected from the group consisting of a silicone hardcoat, silica withhydrolizable silanes, an epoxy, a urethane, an imide, a siloxane and anycombination thereof.
 6. The optical storage medium of claim 3, whereinsaid acrylate is at least one member selected from the group consistingof a poly-methylmethacrylate, a methyl methacrylate-polyimide copolymer,a methyl methacrylate-silicone copolymer, and any combination thereof.7. The optical storage medium of claim 1, wherein said high moduluslayer is in direct contact with a data layer.
 8. The optical storagemedium of claim 1, wherein said high modulus layer is in direct contactwith a film layer.
 9. The optical storage medium of claim 1, wherein thethickness of said high modulus layer is between about 0.01 micrometers(μm) and about 50 micrometers (μm).
 10. The optical storage medium ofclaim 1, wherein said high modulus layer has a modulus that is greateror equal to the modulus of the substrate layer.
 11. An asymmetricoptical storage medium comprising the following layers: at least onesubstrate layer; at least one data layer which is in direct contact withsaid substrate layer; at least one high modulus layer which in directcontact with said data layer, said high modulus layer comprising a curedhigh modulus organic polymer having a tensile modulus of at least 1gigapascal; and at least one thin film layer which is in direct contactwith said high modulus layer.
 12. The optical storage medium of claim11, wherein said substrate layer is a polymeric material comprising atleast one member selected from the group consisting of a thermoplastic,a thermoset, and any combination thereof.
 13. The optical storage mediumof claim 12, wherein said thermoplastic is one member selected from thegroup consisting of a polyester, a polycarbonate, a polystyrene, apolymethylmethacrylate, a polyketone, a polyamide, an aromaticpolyether, a polyether-sulfone, a polyether-imide, a polyether ketone, apolyphenylene ether, a polyphenylene sulfide, and any combinationsthereof.
 14. The optical storage medium of claim 11, wherein said datalayer comprises at least one member selected from the group consistingof a thermoplastic, a thermoset, and any combination thereof.
 15. Theoptical storage medium of claim 11, wherein said high modulus layerfurther comprises at least one member selected from the group consistingof a thermoplastic, a thermoset, and any combination thereof.
 16. Theoptical storage medium of claim 11, wherein said thin film layercomprises at least one member selected from the group consisting of ahomopolymer, a copolymer, a thermoplastic, a thermoset, and any mixturesthereof.
 17. The optical storage medium of claim 16, wherein saidthermoset is spin coated.
 18. A method for decreasing the tilt of anasymmetric optical storage medium, said method comprising an additionstep wherein a high modulus layer is added to the optical storage mediumso that the dimensional stability of said medium is increased, said highmodulus layer comprising a cured high modulus organic polymer having atensile modulus of at least 1 gigapascal.
 19. The method of claim 18,wherein said optical storage medium comprises: at least one substratelayer; at least one data layer which is in direct contact with saidsubstrate layer; at least one high modulus layer which in direct contactwith said data layer, and at least one thin film layer which is indirect contact with said high modulus layer.